The present invention relates to a linear guide apparatus, and more particularly relates to a sealing device for a linear guide apparatus which lubricant can be stably fed to the rolling elements over a long period of time.
Further, the present invention relates to a linear guide apparatus, and more particularly relates to a linear guide apparatus, to the lip portion of the sealing device of which lubricant can be automatically fed, so that the life of the sealing device can be prolonged.
A first conventional example will be described as follows. An example of the conventional linear guide apparatus, which is commonly used, is shown in FIG. 37. This conventional linear guide apparatus includes: a guide rail 1 extending in the axial direction, on the outer surface of which a rolling element rolling groove 3 is formed; and a slider 2 incorporated to the guide rail 1 in such a manner that the slider 2 strides the guide rail 1. The slider 2 is composed of a slider body 2A and end caps 2B attached to both ends of the slider body 2A. On inner side surfaces of both wing portions 4 of the slider body 2A, there are provided rolling element rolling grooves (not shown in the drawing) which are opposed to the rolling element rolling groove 3 formed on the guide rail 1. Also, in the slider body 2A, there are provided rolling element returning paths (not shown) which penetrate thick portions of the wing portions of the slider body 2A. On the other hands, the end caps 2B have curved paths (not shown) which communicate the rolling element rolling grooves of the slider body 2A with the rolling element returning paths formed in parallel to the rolling element rolling grooves. In this way, a circulation circuit of the rolling elements is formed by the rolling element rolling grooves, the rolling element returning paths and the curved paths formed on both sides. For example, a large number of rolling elements composed of steel balls are charged into the circulation circuit in which the rolling elements are circulated.
The slider 2 incorporated to the guide rail 1 is smoothly moved along the guide rail 1 when the rolling elements are rolling in both rolling element grooves which are opposed to each other. While the rolling elements are rolling in this way, they circulate endlessly in the rolling element circulation passages formed in the slider.
As a sealing device to seal an opening between the slider 2 and the guide rail 1 for the purpose of dust protection, as shown in FIG. 38, there are provided side seals 5 on both ends (end faces of the end caps 2B), and also there is provided an under seal 6 on the lower surface of the slider 2. Conventionally, these seals are made of rubber such as NBR (acrylonitrile butadiene rubber). In this connection, reference numeral 7 in FIG. 37 is a grease nipple.
A second conventional example of the linear guide apparatus is disclosed in Unexamined Japanese Patent Publication No. Hei. 6-346919 previously proposed by the present applicant. A third conventional example of the linear guide apparatus is disclosed in Unexamined Japanese Patent Publication No. Hei. 7-35146 previously proposed by the present applicant.
The second conventional example will be described as follows. Between the outer surface of the guide rail and the inner surface of the slider moving along the guide rail, there is provided a seal device having a seal lip portion made of rubber or synthetic resin containing lubricant. The seal lip portion comes into contact with an outer surface of the guide rail and seals a gap formed between the inner surface of the slider and the outer surface of the guide rail. Since the seal lip portion of the seal device is made of rubber or synthetic resin containing lubricant so that the seal lip portion has a self-lubricating property, the lubricant contained in the seal gradually oozes out and is automatically fed to a frictional surface of the seal portion. Therefore, the abrasion of the seal lip portion can be suppressed.
The third conventional example will be described as follows. At least a portion of the layer made of rubber or synthetic resin and a portion of the layer made of rubber or synthetic resin containing lubricant are overlapped and integrally joined. At least, on the layer of rubber or synthetic resin containing lubricant, there is formed a seal lip portion which comes into contact with an outer surface of the guide rail so as to seal a gap formed between the inner surface of the slider and the outer surface of the guide rail. Since the seal lip portion also has a self-lubricating property in this third conventional example, lubricant contained in the seal itself gradually oozes out and is fed to a frictional surface of the seal, so that the abrasion of the lip portion can be suppressed. Since the layers are overlapped as described above in the third conventional example, it is possible to provide the following advantages. When the number and thickness of the overlapped layers are appropriately determined, the mechanical strength of the seal lip portion can be arbitrarily set in accordance with the use of the linear guide apparatus.
As shown in FIGS. 52 to 53B t the sealing device of the second conventional example is described as follows. Lubricant is made to ooze from a surface of the guide rail 1 by the action of contact resistance of the seal 11. Accordingly, there is provided no relief 10a as shown in FIG. 53A in the contact portion 11a shown in FIG. 53B where the seal 11 comes into contact with the guide rail 1, but an area of the portion where the seal 11 comes into contact with the guide rail 1 is increased. Further, there is formed a recessed groove 12 in the contact portion 11a where the seal 11 comes into contact with the guide rail 1, so that the portion 11a is divided into two portions. Then the thus divided portions are contacted with the guide rail 1 by two steps. Therefore, the intrusion of foreign objects can be prevented by the contact of two steps better than the contact of one step. Further, lubricant can be held by the recessed groove 12, so that the sliding property of the seal 11 can be enhanced.
However, the above conventional linear guide apparatus has the following disadvantages.
As the slider 2 runs along the guide rail 1, a quantity of grease previously charged inside the slider 2 is decreased. Therefore, the lubrication between the lip portion of the side seal 5 and the guide rail 1 becomes poor, and also the lubrication between the lip portion of the under seal 6 and the guide rail 1 becomes poor. Due to the poor lubrication, the lip portions gradually wears away. Due to the progress of abrasion, the sealing property is deteriorated, and foreign objects such as cutting chips enter the inside of the slider 2, which shortens the life of the linear guide apparatus in some cases.
When the slider 2 runs and the rolling elements roll, grease can be fed to the rolling element rolling groove 3 of the guide rail 1 via the rolling elements. Accordingly, the abrasion is relatively small in a portion of the lip which comes into contact with the rolling element rolling groove 3. On the other hand, the abrasion tends to increase in a portion of the lip which comes into contact with an upper surface of the rail to which no grease is fed because of poor lubrication. Due to the foregoing, the lip portion wears away and damaged. In this way, the life of the linear guide apparatus is shortened.
From this point of view, when the above second example and the third one are adopted, the abrasion of the seal lip portion can be suppressed since the seal lip portion has a self-lubricating property. However, even in the above conventional examples, the following problems may be encountered. A quantity of lubricant oozing from rubber or synthetic resin containing lubricant is not sufficient to lubricate the balls and rollers which guide the movement of the slider of the linear guide apparatus, that is, it is difficult to maintain smooth rolling motions of the rolling elements such as balls and rollers.
In the sealing device containing lubricant of the above second conventional example or the third one, the seal lip portion is pressed against the guide rail only by the elasticity of the seal itself. Accordingly, it is possible to provide a sufficiently high pressing force as a seal, however, it is impossible to provide a sufficiently high pressing force as a lubricant feed unit.
Further, a shape of each portion of the guide rail 1 with which the seal 11 comes into contact, for example, a shape of the ball rolling groove, the guide rail side surface or the upper surface of the guide rail is complicated, and further the seal 11 is attached being a little displaced. Therefore, it is difficult for the seal 11 to be positively contacted with each portion of the guide rail 1. Accordingly, a sufficient quantity of lubricant can not be provided and the dust protecting property is deteriorated. As a result, the lubricant in the slider 2 is widely diffused.